The subject invention refers to a submersible fuel filter device of suctional type, connectable at the end of a fuel inlet hose in a fuel tank. More precisely the invention refers to a fuel filter device provided with a filter body with an outlet port connected to the inlet hose, and mainly intended for usage in handheld working tools, such as chain saws, which are to be handled in a variety of positions during work.
A submersible fuel filter device of the kind mentioned above, which since a long time has been manufactured and used by the applicant, comprises a coaxial body with a central filtration chamber, which is connected to an outlet port as well as an inlet hose, and outside the filtration chamber there are two coaxial filter walls with an intermediate, annular space containing a metal ring, which serves as a sinker. A limitation with this kind of fuel filter is that the filter surface is small in relation to the outer dimensions of the filter. Furthermore the sinker, which is movable in the annular chamber, could damage the filter.
As an example of the state of the art in the patent literature reference is made to the filter devices described in EP 0 246 036, U.S. Pat. Nos. 4,851,118 and 5,441,637.
A general problem concerning todays fuel filters of the kind specified above is that they are so coarse, i.e. they have so great porosity, that, on the one hand a non-desirable degree of pollution passes through the filter and on the other hand that an essential amount of dirt particles get stuck inside the filter causing that it will be filled up gradually. This leads to frequent service regarding cleaning and changing of fuel filter and also it seems to increase the wear of the engine.
Fuel filter devices of the kind mentioned in the preamble are mass-produced articles and used in a number of movable and/or portable machines run by an internal combustion engine, such as lawn movers, chain saws, power cutters, brush cutters, grass trimmers etc. A purpose of the invention is to offer a submersible fuel filter device of the kind mentioned above, provided with a filter, which is designed so that it provides a large, active filter surface in combination with a fine porosity and still very small outer dimensions. Besides the fact that the filter device thereby gets the possibility to comply with the high functional demands, such as filtration capability, durability etc., it should also be designed so that it enables a simple and low cost mass production. Both these requirements, i.e. adequate function and simple/low cost design, have not earlier been possible to combine in a satisfactory way. The first purpose of the subject invention is to solve this problem. This and other purposes can be achieved in that the invention is having the characteristics appearing from the independent claim. In this manner a relatively large filter surface of a cup-shaped filter body with small material thickness has been combined with a filter material with extremely fine porosity, i.e. less than 10 xcexcm. Preferably a porosity less than or equal to 5 xcexcm is used. Traditionally such a fine porosity of a filter body of moderate size is considered to result in a too high flow resistance when the filter is new, as well as the filter will be filled up very quickly. Normally a filter material with a porosity between 20 xcexcm and 80 xcexcm is used for this type of filter. However, at testings it has turned out, which is surprising, that the filter according to the invention was filled up much more slowly than a conventional filter. And at the same time the flow resistance could be mastered. The mechanism behind this matter of fact is considered to be that almost the total amount of dirt particles are being built up on the filter surface and will not get stuck inside the filter material. This in combination with a high degree of self-cleansing through fuel wash in the tank as well as washing in connection with tank fillings seems to be the explanation to the extremely good results obtained. About 10 times longer lifetime for this filter is obtained compared to a conventional filter. And at the same time a considerably more thorough filtration is obtained. The applicant doesn""t know of any filter of this kind having such an extremely fine porosity. On the other hand there exist two-stage filters having a more coarse prefilter as well as a more fine main filter and with a porosity of approximately 5-15 xcexcm. In that case the main filter is a so called xe2x80x9cvolume filterxe2x80x9d, where the fuel in an axial direction flows through a long filter block located in the fuel pipe. The filter block is gradually being filled up by the dirt particles which have passed through the prefilter. For obvious reasons this xe2x80x9cvolume filterxe2x80x9d could hardly have any self-cleansing capacity. Further purposes, characteristics and aspects of the invention will become apparent from the submitted claims and from the following description of some preferred embodiments.